Module balancing for a mixed chemistry battery

Abstract

Embodiments include balancing modules during charging of a mixed chemistry battery pack having a first battery module connected in series to a second battery module. Aspects include monitoring a first state-of-charge (SOC) of the first battery module having a first battery chemistry and monitoring a second SOC of the second battery module having a second battery chemistry. Aspects also include selectively activating one of a first bypass switch and a first activation switch of the first battery module based on the first SOC and the second SOC and selectively activating one of a second bypass switch and a second activation switch of the second battery module based on the first SOC and the second SOC. The activation of the first bypass switch prevents the first battery module from charging and activation of the second bypass switch prevents the second battery module from charging.

What is claimed is: 
     
         1 . A method for balancing modules during charging of a mixed chemistry battery pack having a first battery module connected in series to a second battery module, the method comprising:
 monitoring a first state-of-charge (SOC) of the first battery module having a first battery chemistry;   monitoring a second SOC of the second battery module having a second battery chemistry that is different than the first battery chemistry;   selectively activating one of a first bypass switch and a first activation switch of the first battery module based on the first SOC and the second SOC; and   selectively activating one of a second bypass switch and a second activation switch of the second battery module based on the first SOC and the second SOC, wherein activation of the first bypass switch prevents the first battery module from charging and activation of the second bypass switch prevents the second battery module from charging.   
     
     
         2 . The method of  claim 1 , wherein the first battery chemistry is nickel-manganese cobalt and the second battery chemistry is lithium iron phosphate. 
     
     
         3 . The method of  claim 1 , wherein the first bypass switch and the second bypass switch are deactivated and the first activation switch and the second activation switch are activated based on a determination that the first SOC and the second SOC are less than one. 
     
     
         4 . The method of  claim 1 , wherein the first bypass switch and the second bypass switch are activated and the first activation switch and the second activation switch are deactivated based on a determination that the first SOC and the second SOC are equal to one. 
     
     
         5 . The method of  claim 1 , wherein the first activation switch is activated, the first bypass switch is deactivated, the second activation switch is deactivated, and the second bypass switch is activated based on a determination that the first SOC is less than one and the second SOC is equal to one. 
     
     
         6 . The method of  claim 1 , wherein the first activation switch is deactivated, the first bypass switch is activated, the second activation switch is activated, and the second bypass switch is deactivated based on a determination that the second SOC is less than one and the first SOC is equal to one. 
     
     
         7 . The method of  claim 1 , wherein the selective activation of the first bypass switch, the first activation switch, the second bypass switch, and the second activation switch are based on a flag value that is calculated based on the first SOC, a first capacity of the first battery module, the second SOC, a second capacity of the second battery module, and a capacity difference of the first battery module and the second battery module. 
     
     
         8 . A vehicle comprising:
 a mixed chemistry battery comprising:
 a first battery cell having a first chemistry; 
 a first activation switch connected to the first battery cell, wherein activation of the first activation switch enables charging of the first battery cell; 
 a first bypass switch connected to the first battery cell, wherein activation of the first bypass switch prevents the first battery cell from charging; 
 a second battery cell connected to the first battery cell in series, the second battery cell having a second chemistry that is different than the first chemistry; 
 a second activation switch connected to the second battery cell, wherein activation of the second activation switch enables charging of the second battery cell; 
 a second bypass switch connected to the second battery cell, wherein activation of the second bypass switch prevents the second battery cell from charging; and 
   a controller configured to:
 monitor a first state-of-charge (SOC) of the first battery cell and a second SOC of the second battery cell; 
 selectively activate one of the first bypass switch and the first activation switch based on the first SOC and the second SOC; and 
 selectively activate one of the second bypass switch and the second activation switch based on the first SOC and the second SOC. 
   
     
     
         9 . The vehicle of  claim 8 , wherein the first chemistry is nickel-manganese cobalt and the second chemistry is lithium iron phosphate. 
     
     
         10 . The vehicle of  claim 8 , wherein the first bypass switch and the second bypass switch are deactivated and the first activation switch and the second activation switch are activated by the controller based on a determination that the first SOC and the second SOC are less than one. 
     
     
         11 . The vehicle of  claim 8 , wherein the first bypass switch and the second bypass switch are activated and the first activation switch and the second activation switch are deactivated by the controller based on a determination that the first SOC and the second SOC are equal to one. 
     
     
         12 . The vehicle of  claim 8 , wherein the first activation switch is activated, the first bypass switch is deactivated, the second activation switch is deactivated, and the second bypass switch is activated by the controller based on a determination that the first SOC is less than one and the second SOC is equal to one. 
     
     
         13 . The vehicle of  claim 8 , wherein the first activation switch is deactivated, the first bypass switch is activated, the second activation switch is activated, and the second bypass switch is deactivated by the controller based on a determination that the second SOC is less than one and the first SOC is equal to one. 
     
     
         14 . The vehicle of  claim 8 , wherein the selective activation of the first bypass switch, the first activation switch, the second bypass switch, and the second activation switch are based on a flag value that is calculated based on the first SOC, a first capacity of the first battery cell, the second SOC, a second capacity of the second battery cell, and a capacity difference of the first battery cell and the second battery cell. 
     
     
         15 . A vehicle comprising:
 a mixed chemistry battery comprising:
 a first battery cell having a first chemistry; 
 a first discharge switch connected to the first battery cell and to a first resister, wherein activation of the first discharge switch causes dissipation of charge from the first battery cell; 
 a second battery cell connected to the first battery cell in series, the second battery cell having a second chemistry that is different than the first chemistry; 
 a second discharge switch connected to the second battery cell and to a second resister, wherein activation of the second discharge switch causes dissipation of charge from the second battery cell; and 
   a controller configured to:
 monitor a first state-of-charge (SOC) of the first battery cell and a second SOC of the second battery cell; 
 selectively activate the first discharge switch and the second discharge switch based on the first SOC and the second SOC. 
   
     
     
         16 . The vehicle of  claim 15 , wherein the first chemistry is nickel-manganese cobalt and the second chemistry is lithium iron phosphate. 
     
     
         17 . The vehicle of  claim 15 , wherein the selective activation of a first discharge switch and the second discharge switch are based on a flag value that is calculated by: 
       
         
           
             
               Flag 
               = 
               
                 
                   ( 
                   
                     
                       S 
                       ⁢ 
                       O 
                       ⁢ 
                       
                         
                           C 
                           1 
                         
                         · 
                         
                           C 
                           1 
                         
                       
                     
                     - 
                     
                       C 
                       D 
                     
                   
                   ) 
                 
                 - 
                 
                   S 
                   ⁢ 
                   O 
                   ⁢ 
                   
                     
                       C 
                       2 
                     
                     · 
                     
                       C 
                       2 
                     
                   
                 
               
             
           
         
         where SOC 1  is the first SOC, SOC 2  is the second SOC, C 1  is a total capacity of the first battery cell, C 2  is a total capacity of the second battery cell, and C D  is a difference between C 1  and C 2 . 
       
     
     
         18 . The vehicle of  claim 17 , wherein the first discharge switch is activated and the second discharge switch is deactivated by the controller based on a determination that the flag value is greater than zero. 
     
     
         19 . The vehicle of  claim 17 , wherein the first discharge switch is deactivated and the second discharge switch is activated by the controller based on a determination that the flag value is less than zero. 
     
     
         20 . The vehicle of  claim 17 , wherein the first discharge switch and the second discharge switch are deactivated by the controller based on a determination that the flag value is equal to zero.